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451 [689] HELLRIEGEL MARSH
in either case. In this case, an irrational number is as useful as, and no more mysterious than, a rational number. Dedekind lived out a quiet, long life. He never married. [689] HELLRIEGEL, Hermann (hel'ree- gel)
German chemist Born: Mausitz, Saxony, October 21, 1831 Died: Bemburg, Anhalt-Bern burg, September 24, 1895 Hellriegel studied chemistry at the Forestry Academy near Dresden, and he interested himself in the nutritional re quirements of plants. This was the sort of knowledge that would make it possi ble to fertilize marginally fertile soils with greater efficiency. He was particularly interested in sugar beets, and their nitrogenous require ments. In the course of these investi gations he discovered that certain legu minous plants (e.g., peas, beans) were capable of making use of atmospheric nitrogen, something most plants cannot do. This meant that planting such le gumes tended to refertilize soils as far as nitrogen was concerned without the ad dition of chemical fertilizers. This dis covery was announced in 1886. [690] MARSH, Othniel Charles American paleontologist
tober 29, 1831 Died: New Haven, Connecticut, March 18, 1899 Marsh, the son of a shoe manufac turer, was brought up by a rich uncle, George Peabody, by whose will he was eventually made independently wealthy. He studied at Yale, graduating in 1860. He grew interested in natural history and persuaded his uncle to endow the Pea body Natural History Museum at Yale in 1866. In that year Marsh was appointed a professor of vertebrate paleontology (the study of extinct forms of life of past geologic eras) at Yale, the first profes sorship of the sort to be established in the United States. Marsh, with William F. Cody (“Buffalo Bill”) as a guide, scoured the western United States for fossils, sparing no expense and, in fact, spending a quarter of a million dollars. He never married and had no family who might have needed the money. He competed with Cope [748] in this task of fossil discovery and between these two paleontologists there grew up a bitter and unforgiving enmity. They raced for fossils almost more to spite each other than to advance science, dis puted priority on every possible occa sion, and, if that failed, disputed conclu sions. It was a rather unedifying specta cle, but on the other hand neither might have accomplished as much without the other’s provocation. The net result was that startling fossil evidence was discov ered that made particularly dramatic Darwin’s [554] theory of evolution. Marsh, a strong Darwinian, uncovered enough specimens of different forms of ancestral horses to make it quite possible to work out a complete line of descent for the creature. Cope, in the early 1870s, competed desperately in this and between the two such a picture of equine evolution was worked out as virtually to catch Darwinism in action. In the early 1870s Marsh dug dra matic fossil remnants from the Kansas rocks. He found an extinct bird so primi tive that it still retained its reptilian teeth (which no living bird possesses) so that it was clearly marked as a “missing link” between reptile and bird. This lent credi bility to the evolution of the latter from the former. This same bird, the Hes- peromis (“western bird”), so soon after the first development of feathered flight, had already lost its wings and, pen guinlike, returned to the sea. Marsh also discovered pterodactyls, flying lizards of the Cretaceous era, working out the nature of the first from a single leg bone, together with some of the large land reptiles of the period. This turned his attention to the dinosaurs, which, by all odds, are the most dra matic examples of extinct life. The in
[691] v o n
v o n [691] creasing familiarity of the general public with the bony remnants of these gigan tic, small-brained creatures probably did more than anything else to create the necessary atmosphere for the acceptance of evolution. In the end Marsh had de scribed eighty new kinds of saurians and over five hundred new fossil species alto gether. He was president of the National Academy of Sciences from 1883 to 1895.
[691] VOIT, Karl von German physiologist Born: Amberg, Bavaria, October 31, 1831 Died: Munich, Bavaria, January 31, 1908 Voit, the son of an architect, was an other man lured to chemistry by the at tractions of Liebig [532], (Wohler [515] was another of his teachers.) Originally intending to make medicine his profes sion, and obtaining his medical degree in 1854, Voit veered off course to concern himself with the chemical aspects of the human body, particularly the chemical fate of the various foodstuffs after absorption into the body. He was one of the founders of this branch of biochem istry. In 1863 he became a professor of physiology at the University of Munich and remained there for the rest of his life.
Until his time, chemists, including Lie big himself, thought the various food stuffs contributed energy for specific functions; that protein, for instance, was the specific source of energy for muscu lar work. In 1861 Voit showed that this was not so, that the rate at which pro teins were broken down in the body did not increase during muscular work. In 1865 he was able to develop lines of experimentation that indicated food stuffs did not combine directly with oxy gen to form carbon dioxide and water. Rather, they underwent a long chain of reactions during which a succession of intermediate products were evanescently formed. The net result, to be sure, was indeed carbon dioxide and water; but the pathway to those end products was com plex indeed. This was the introduction of biochem ists to the concept of intermediary me tabolism. Much of the work in biochem istry in the century since has been the slow and patient elucidation of the de tails in the various chains of reactions. Some of the details were worked out by Voit himself. For instance, it was known that the starchlike substance gly cogen, discovered a generation earlier by Bernard [578], was built up out of glu cose units. In 1891 Voit was able to show that mammals stored glycogen not only when they were supplied with glu cose but also when sucrose, fructose, or maltose (three other sugars) were in their diet in place of glucose. The logical conclusion was that the mammalian body could convert sucrose, fructose, and maltose into glucose. It was also Voit who in the 1870s, fol lowing one of Liebig’s suggestions, devel oped the test for studying nitrogen in take and output. When protein is broken down, the waste product, urea, is formed and excreted in the urine. By matching the nitrogen contained in the urea ex creted with that contained in the protein ingested, Voit could tell the state of the nitrogen balance; that is, whether the body was storing nitrogen, losing nitro gen, or keeping the balance even. He worked with diets in which one particular protein was the sole nitrogen- containing item in the diet and found that with some the animals would go into negative nitrogen balance; it would excrete more nitrogen than it took in. This particular protein apparently could not be utilized for building tissue and was broken down for energy, the nitro gen portion being excreted. This, added to nitrogen loss through normal wear- and-tear of the proteins constituting the tissues, produced the negative values. In the long run, with such a protein the sole source of nitrogen, the animal must waste away and die, and Voit showed that gelatin was one of these “incomplete proteins.” This line of research led even tually to the discovery of the essential amino acids and the climactic work of Rose [1114] a half century later. Voit studied the human being as a unit in one sense, for with the help of Pet-
[692] MAXWELL
MAXWELL [692] tenkofer [612] he devised a calorimeter large enough to enclose a human being. (Previous instruments of the sort could only be used for smaller animals.) In this manner the oxygen consumed, the carbon dioxide liberated, and the heat produced by a human being could all be carefully measured. From 1866 to 1873 he was able to study man’s overall rate of metabolism under various conditions. The resting or basal metabolic rate (BMR) could thus be determined for the first time in human beings. This later proved of value in diagnosing abnormal thyroid conditions. Voit’s pupil Rubner [848] continued this form of calorimetry, carrying it to an amazing pitch of accu racy. [692] MAXWELL, James Clerk Scottish mathematician and physicist Born: Edinburgh, November 13, 1831
Died: Cambridge, England, November 5, 1879 Maxwell, born of a well-known Scottish family, was an only son. His mother died of cancer when he was eight, but except for that, he had a happy childhood. He early showed signs of mathe matical talent. The possession of such talent is, alas, easily mistaken for fool ishness by ordinary young men and young Maxwell was nicknamed Daffy by his classmates. At the age of fifteen he contributed a piece of original work on the drawing of oval curves to the Royal Society of Edinburgh. The work was so well done that many refused to believe such a young boy could be the author. The next year Maxwell met the aged Nicol [394], who had invented the po larizing Nicol prism. As a result he grew interested in the phenomena of light gen erally. Later he was to apply this interest by making use of the Young [402]- Helmholtz [631] theory of color percep tion in order to suggest methods eventu ally used in color photography. At Cambridge, which he entered in 1850, he graduated second in his class in mathematics, as Kelvin [652] had done before him and J. J. Thomson [869] was to do after him. The student who finished in first place became an eminent mathematician but never achieved Max well’s fame. Maxwell was appointed to his first professorship at Aberdeen in 1856. In 1857 Maxwell made his major con tribution to astronomy in connection with Saturn’s rings. At the time, there was considerable uncertainty as to the nature of those rings. In appearance, they seemed like flat, hollow discs. Max well showed, from theoretical consid erations, that if the rings were actually solid or liquid, the gravitational and me chanical forces upon them as they ro tated would break them up. However, if they consisted of numerous small solid particles, they would give the appearance (from Saturn’s vast distance) of being solid and would be dynamically stable, too. Cassini [209] had actually guessed this a century and a half earlier and all evidence since his time had strengthened Maxwell’s view. The rings do indeed consist of myriads of small bodies, mak ing a very dense kind of “asteroid belt” about the planet. About 1860 Maxwell brought his mathematics to bear upon another prob lem involving many tiny particles, this time the particles making up gases, rather than Saturn’s rings. Every gas is made up of molecules in rapid motion in various directions. Maxwell treated the situation statistically as Bernoulli [268] had tried to do a century before. Max well had more powerful mathematical tools at his disposal, however, and could go much further than Bernoulli had been able to do. He considered the molecules as moving not only in all directions but at all velocities, and as bounding off each other and off the walls of the container with perfect elasticity. Along with Boltz mann [769], who was also working on the problem at this time, he worked out the Maxwell-Boltzmann kinetic theory of gases.
An equation was evolved that showed the distribution of velocities among the molecules of a gas at a particular tem perature. A few molecules moved very slowly and a few very quickly but larger 4 5 4
[692] MAXWELL
MAXWELL [692] percentages moved at intermediate veloc ities, with a most common velocity somewhere in the middle. A rise in tem perature caused the average velocity to rise, while a drop in temperature caused it to fall. In fact, temperature, and heat itself, could be pictured as involving mo lecular movement and nothing else. This was the final blow to heat as an impon derable fluid. The notion of Rumford [360] that heat was a form of motion was established once and for all. Maxwell, to emphasize the difference between the fluid theory of heat and the moving-molecule theory of heat, in vented, in 1871, what is popularly called Maxwell’s demon. In the fluid theory, heat could flow only from a warm body to a cold, the reverse flow being incon ceivable in the light of Clausius’ [633] second law of thermodynamics. In the moving-molecule theory, how ever, individual molecules in a gas at equilibrium temperature would have a whole spectrum of velocities from very slow to very fast. If two containers of gas at the same temperature were con nected by a tiny door guarded by a tiny demon, one could imagine that door being opened whenever a slowly moving molecule was passing to the right, but not to the left; or whenever a quickly moving molecule was passing to the left, but not to the right. In this way the gas molecules would accumulate in the left flask, which would thus grow hotter and hotter while the slow molecules would accumulate in the right flask, which would grow colder and colder. Heat would flow in this fashion continuously from cold to hot in defiance of the sec ond law. Of course, Maxwell’s demon doesn’t exist, but the random operations of chance could conceivably bring about such a situation somewhere, given enough time. This conversion of the sec ond law of thermodynamics from a cer tain flow to merely a highly probable distribution of velocities is important philosophically. It means, for instance, that the “heat death” of the universe, in which entropy reaches its maximum, might conceivably not be inevitable and, even if reached, might not be eternal. The new view of heat did not invali date the thermodynamic work of men such as Carnot [497]. Their conclusions, based on observation and experiment, were merely explained on the basis of a new and better theory and remained as useful and worthwhile as ever. In 1871 Maxwell reluctantly allowed himself to be appointed professor of ex perimental physics at Cambridge. He was the first to hold a professorship in the subject, though it must be admitted he was not a great success as a lecturer. He went over the heads of most and usu ally had an audience of no more than three or four. A few, who were brainy enough, J. J. Thomson for one, were in spired by the lectures. While at Cambridge he organized the Cavendish Laboratory, named in honor of the eccentric English scientist Henry Cavendish [307] of the previous century and served as its director until his death. He also contributed considerable sums of his own to keep it going. A generation later the Cavendish Laboratory was to do great work in connection with radio activity. The crowning work of Maxwell’s life was carried on between 1864 and 1873, when he placed into mathematical form the speculations of Faraday [474] con cerning magnetic lines of force. (Max well resembled Faraday, by the way, in possessing deep religious convictions and in having a childless, but very happy, marriage.) In working on the concept of lines of force, Maxwell was able to work out a few simple equations that expressed all the varied phenomena of electricity and magnetism and bound them indissolubly together. Maxwell’s theory showed that electricity and magnetism could not exist in isolation. Where one was, so was the other, so that his work is usually referred to as the electromagnetic theory. He showed that the oscillation of an electric charge produced an electromag netic field that radiated outward from its source at a constant speed. This speed could be calculated by taking the ratio of certain units expressing magnetic phe nomena to units expressing electrical phenomena. This ratio worked out to be
[692] MAXWELL
FRIEDEL [693] just about 300,000 kilometers per sec ond, or 186,300 miles per second, which is approximately the speed of light (for which the best available figure at present is 299,792.5 kilometers per second or 186,282 miles per second). To Maxwell this seemed more than one had a right to expect of coincidence and he suggested that light itself arose through an oscillating electric charge and was therefore an electromagnetic ra diation. In his time, no oscillating charge was known that could possibly give rise to light and it was left for Zeeman [945] a generation later to prove Maxwell’s point in this connection. Furthermore, since charges could os cillate at any velocity, it seemed to Max well that there should be a whole family of electromagnetic radiations of which visible light was only a small part. Over half a century earlier, to be sure, Herschel [321] had discovered infrared light just beyond the red end of the visi ble spectrum and Ritter [413] had dis covered ultraviolet light, just beyond the violet end. Since then, Stokes [618] had shown that ultraviolet light had all the properties of ordinary light and Melloni [504] had done the same for infrared. However, Maxwell predicted radiations far beyond both the infrared and the ul traviolet. This was not to be verified until the time of Hertz [873]. Maxwell believed that not only were the waves of electromagnetic radiation carried by the ether, but the magnetic lines of force were actually disturbances of the ether. In this way he conceived he had abolished the notion of “action at a distance.” It had seemed to some experi menters in electricity and magnetism, Ampère [407], for instance, that a mag net attracted iron without actually mak ing contact with the iron. To Maxwell it seemed that the disturbances in the ether set up by the magnet touched the iron and that everything could be worked out as “action on contact.” (Not everyone accepted this. Airy [523] strenuously op posed the concept.) In one respect, however, Maxwell’s in tuition was at fault. He rejected the no tion that electricity was particulate in na ture, even though that was so strongly suggested by Faraday’s laws of electrol ysis.
Almost the last accomplishment of Maxwell’s was his publication of the hitherto unpublished electrical experi ments of Cavendish, showing that strange man to have been fifty years ahead of his time in his work. Maxwell was also among the first to appreciate the work of Gibbs [740]. Maxwell died, before the age of fifty, of cancer. Had he lived out what would today be considered a normal life expec tancy he would have seen his prediction of a broad spectrum of electromagnetic radiation verified by Hertz. However, he would also have seen the ether, which his theory had seemed to establish firmly, brought into serious question by the epoch-making experiment of Michel- son [835] and Morley [730], and he would have seen electricity proved to consist of particles after all. His elec tromagnetic equations did not depend on his own interpretations of the ether, however, and he had wrought better than he knew. When Einstein’s [1064] theories, a generation after Maxwell’s death, upset almost all of “classical phys ics,” Maxwell’s equations remained un touched—as valid as ever. [693] FRIEDEL, Charles (free-del') French chemist
March 12, 1832 Died: Montauban, Tarn-et- Garonne, April 20, 1899 Friedel, who had Pasteur [642] as one of his teachers, became professor of min eralogy at the Sorbonne in Paris in 1876, the year before he and Crafts [741] im mortalized themselves by discovering the Friedel-Crafts reaction. (The American pronunciation shifts the accent of Frie- del’s name to the first syllable.) He was also interested in mineralogical chemistry, naturally, and was one of those who attempted to make synthetic diamonds, though unlike Moissan [831] he was never under the illusion that he had succeeded. Download 17.33 Mb. Do'stlaringiz bilan baham: 
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